heat transfer, heat exchangers,...

HEAT TRANSFER, HEAT

EXCHANGERS,

CONDENSORS AND

REBOILERS, AIR

COOLERS

ReyadAwwad Shawabkeh

Associate Professor of Chemical Engineering

King Fahd University of Petroleum & Minerals

Dhahran, 31261Kingdom of Saudi Arabia

1

Contents� HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS 2

� HEAT TRA NSFER BY CONDUCTION 3� The Heat Conduction Equation 9

� HEAT TRA NSFER BY CONVECTION 12� Forced Convection 12� Natural Convection 14

� HEAT TRA NSFER BY RADIATION 15� OVERALL HEAT TRA NSFER COEFFICIENT 18

� PROBLEMS 22

� DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS 23

� SIZE NUM BERI NG A ND NAMING 23� SIZING AND DIMENSION 27� TUBE-SIDE DESIGN 32� SHELL-SIDE DESIGN 33� Baffle type and spacing 33

� GENERAL DESIGN CONSIDERATION 35

� THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN 37

� DESIGN OF SINGLE PHASE HEAT EXCHA NGER 37� Kern’s Method 45� Bell’s method 49� Pressure drop inside the shell and tube heat exchanger 57

� DESIGN OF CONDENSERS 65� DESIGN OF REBOILER AND VAPORIZERS 72� DESIGN OF AIR COOLERS9 85

� MECHANICAL DESIGN FOR HEAT EXCHANGERS10 88

� DESIGN LOADINGS 88� TUBE-SHEET DESIGN AS PER TEMA STA NDA RDS 90� DESIGN OF CYLINDRICA L SHELL, END CLOSURES AND FORCED HEA D 91

� REFERENCES 95

2

HEAT TRANSFER LAW APPLIED TO

HEAT EXCHANGERS3

Heat Transfer by Conduction

W/m2 W/m.K

4

Thermal Conductivity of solids 5

Thermal Conductivity of liquids 6

Thermal conductivity of gases 7

Example

Calculate the heat flux within a copper rod that

heated in one of its ends to a temperature of 100 oC

while the other end is kept at 25 oC. The rode length

is 10 m and diameter is 1 cm.

8

Example

An industrial freezer is designed to operate with an internal air

temperature of -20 oC when external air temperature is 25 oC. The walls

of the freezer are composite construction, comprising of an inner layer of

plastic with thickness of 3 mm and has a thermal conductivity of 1 W/m.K.

The outer layer of the freezer is stainless steel with 1 mm thickness and

has a thermal conductivity of 16 W/m.K. An insulation layer is placed

between the inner and outer layer with a thermal conductivity of 15

W/m.K. what will be the thickness of this insulation material that allows a

heat transfer of 15 W/m2 to pass through the three layers, assuming the

area normal to heat flow is 1 m2?

9

The Heat Conduction Equation

Rate of heat

generation

inside control

volume

Rate of energy

storage inside

control volume

Rate of heat conduction

into control volume

+ =

Rate of heat

conduction

out of control

volume

+

10

The Heat Conduction Equation11

Heat Transfer by Convection 12

Reynolds and Prandtl Numbers

Values of Prandtl number for different liquids and gases

Re < 2100 Laminar flow

Re > 2100 Turbulent flow

13

Flow through a single smooth cylinder

This correlation is valid over the ranges 10 < Rel < 107 and 0.6 < Pr < 1000 where

14

Flow over a Flat Plate

Re < 5000 Laminar flow

Re > 5000 Turbulent flow

15

Natural Convection16

Heat Transfer by Radiation

q = ε σ (Th4 - Tc

4) Ac

Th = hot body absolute temperature (K)

Tc = cold surroundings absolute temperature (K)

Ac = area of the object (m2)

σ = 5.6703 10-8 (W/m2K4)

The Stefan-Boltzmann Constant

17

Emissivity coefficient for several selected material

Surface MaterialEmissivity Coefficient

- ε -

Aluminum Commercial sheet 0.09

Aluminum Foil 0.04

Aluminum Commercial Sheet 0.09

Brass Dull Plate 0.22

Brass Rolled Plate Natural Surface 0.06

Cadmium 0.02

Carbon, not oxidized 0.81

Carbon filament 0.77

Concrete, rough 0.94

Granite 0.45

Iron polished 0.14 - 0.38

Porcelain glazed 0.93

Quartz glass 0.93

Water 0.95 - 0.963

Zink Tarnished 0.25

18

Overall heat transfer coefficient

For a wall

For cylindrical

geometry

19

Typical value for overall heat transfer coefficient

Shell and Tube

Heat ExchangersHot Fluid Cold Fluid U [W/m2C]

Heat Exchangers Water Water 800 - 1500

Organic solvents Organic Solvents 100 - 300

Lightoils Lightoils 100 - 400

Heavy oils Heavy oils 50 - 300

Reduced crude Flashed crude 35 - 150

Regenerated DEA Foul DEA 450 - 650

Gases (p = atm) Gases (p = atm) 5 - 35

Gases (p = 200 bar) Gases (p = 200 bar) 100 - 300

Coolers Organic solvents Water 250 - 750

Lightoils Water 350 - 700

Heavy oils Water 60 - 300

Reduced crude Water 75 - 200

Gases (p = 200 bar) Water 150 - 400

Organic solvents Brine 150 - 500

Water Brine 600 - 1200

Gases Brine 15 - 250

20

Heat Exchangers Hot Fluid Cold Fluid U [W/m2C]

Heaters Steam Water 1500 - 4000

Steam Organic solvents 500 - 1000

Steam Lightoils 300 - 900

Steam Heavy oils 60 - 450

Steam Gases 30 - 300

HeatTransfer (hot) Oil Heavy oils 50 - 300

Flue gases Steam 30 - 100

Flue gases Hydrocarbon vapors 30 -100

Condensers Aqueous vapors Water 1000 - 1500

Organic vapors Water 700 - 1000

Refinery hydrocarbons Water 400 - 550

Vapors with some non

condensableWater 500 - 700

Vacuum condensers Water 200 - 500

Vaporizers Steam Aqueous solutions 1000 - 1500

Steam Lightorganics 900 - 1200

Steam Heavy organics 600 - 900

HeatTransfer (hot) oil Refinery hydrocarbons 250 - 550

21

DESIGN STANDARDS FOR

TUBULAR HEAT EXCHANGERS

• Size of heat exchanger is represented by the shell inside

diameter or bundle diameter and the tube length

• Type and naming of the heat exchanger is designed by three letters single pass shell

The first one describes the stationary head type

The second one refers to the shell type

The third letter shows the rear head type

TYPE AES refers to Split-ring floating head exchanger with removable

channel and cover.

22

Heat exchanger nomenclatures23

The standard nomenclature for shell and tube heat exchanger

1. Stationary Head-Channel

2. Stationary Head-Bonnet

3. Stationary Head Flange-Channel or

Bonnet

4. Channel Cover

5. Stationary Head Nozzle

6. Stationary Tube sheet

7. Tubes

8. Shell

9. Shell Cover

10. Shell Flange-Stationary Head End

11. Shell Flange-Rear Head End

12. Shell Node

13. Shell Cover Flange

14. Expansion Joint

15. Floating Tube sheet

16. Floating Head Cover

17. Floating Head Cover Flange

18. Floating Head Backing Device

19. Split Shear Ring

20. Slip-on Backing Flange

21. Floating Head Cover-External

22. Floating Tube sheet Skirt

23. Packing Box

24. Packing

25. Packing Gland

26. Lantern Ring

27. Tie-rods and Spacers

28. Support Plates

29. Impingement Plate

30. Longitudinal Baffle

31. Pass Partition

32. Vent Connection

33. Drain Connection

34. Instrument Connection

35. Support Saddle

36. Lifting Lug

37. Support Bracket

38. Weir

39. Liquid Level Connection

40. Floating Head Support

24

Removable cover, one pass, and floating head heat exchanger

Removable cover, one pass, and outside packed floating head heat exchanger

25

Channel integral removable cover, one pass, and outside packed

floating head heat exchanger

26

Removable kettle type reboiler with pull through floating head

27

Gauge(B.W.G.)(inches)

(B.W.G.)(mm) Gauge

(B.W.G.)(inches)

(B.W.G.)(mm)

00000 (5/0) 0.500 12.7 23 0.025 0.6

0000 (4/0) 0.454 11.5 24 0.022 0.6000 (3/0) 0.425 10.8 25 0.020 0.500 (2/0) 0.380 9.7 26 0.018 0.5

0 0.340 8.6 27 0.016 0.41 0.300 7.6 28 0.014 0.42 0.284 7.2 29 0.013 0.33 0.259 6.6 30 0.012 0.34 0.238 6.0 31 0.010 0.35 0.220 5.6 32 0.009 0.26 0.203 5.2 33 0.008 0.27 0.180 4.6 34 0.007 0.2

8 0.165 4.2 35 0.005 0.19 0.148 3.8 36 0.004 0.1

10 0.134 3.4 25 0.020 0.511 0.120 3.0 26 0.018 0.5

12 0.109 2.8 27 0.016 0.413 0.095 2.4 28 0.014 0.4

14 0.083 2.1 29 0.013 0.315 0.072 1.8 30 0.012 0.316 0.065 1.7 31 0.010 0.317 0.058 1.5 32 0.009 0.218 0.049 1.2 33 0.008 0.219 0.042 1.1 34 0.007 0.220 0.035 0.9 35 0.005 0.121 0.032 0.8 36 0.004 0.122 0.028 0.7

Tube sizing: Birmingham Wire Gage28

29Tube sizing: Birmingham Wire Gage

Tube-side design

Arrangement of tubes inside the heat exchanger

30

Shell-side design

types of shell passes(a) one-pass shell for E-type, (b) split flow of G-type,

(c) divided flow of J-type, (d) two-pass shell with longitudinal baffle of F-type

(e) double split flow of H-type.

31

Shell-side design

Shell thickness for different diameters and material of constructions

32

Baffle type and spacing33

General design consideration

Factor Tube-side Shell-side

Corrosion More corrosive fluid Less corrosive fluids

Fouling Fluids with high fouling

and scaling

Low fouling and scaling

Fluid temperature High temperature Low temperature

Operating pressure Fluids with low pressure

drop

Fluids with high pressure

drop

Viscosity Less viscous fluid More viscous fluid

Stream flow rate High flow rate Low flow rate

34

THERMAL AND HYDRAULIC

HEAT EXCHANGER DESIGN

Design of Single phase heat exchanger

Design of Condensers

Design of Reboiler and Vaporizers

Design of Air Coolers

35

Design of Single phase heat

exchanger

36

Typical values for fouling factor coefficients37

Temperature profile for different types of

heat exchangers

38

For counter current

For co-current

39

one shell pass; two or more even tube 'passes

40

two shell passes; four or multiples of four tube passes

divided-flow shell; two or more even-tube passes

41

split flow shell, 2 tube pass

cross flow heat exchanger

42

Shell-side heat transfer coefficient 43

Shell diameter 45

Bundle diameter clearance

47

Tube-side heat transfer coefficient 48

Tube-side heat transfer factor

49

Shell and Tube design procedure

• Kern’s Method

• Bell’s method

This method is designed to predict the local heat transfer coefficient and pressure drop by incorporating the effect of leak and by-passing inside the

shell and also can be used to investigate the effect of constructional tolerance and the use of seal strip

This method was based on experimental work on commercial exchangers with standard tolerances and will give a reasonably satisfactory prediction

of the heat-transfer coefficient for standard designs.

50

Kern’s Method 51

Bell’s method 52

56

Figure 34 Baffle cut geometry

Pressure drop inside the shell 59

Pressure drop inside the tubes 60

61Design of Condensers

Direct contact cooler

• For reactor off-gas quenching

• Vacuum condenser

• De-superheating

• Humidification

• Cooling towers

62Condensation outside horizontal tubes

For turbulent flow,

For Laminar flow

63Condensation inside horizontal tubes

stratified flow

annular flow

64Design of Reboiler and Vaporizers

Forced-circulation reboiler

Thermosyphon reboiler

Kettle reboiler

• Suitable to carry viscous and heavy fluids. • Pumping cost is high

• The most economical type where there is no need for pumping of the fluid

• It is not suitable for viscous fluid or high vacuum operation

• Need to have a hydrostatic head of the fluid

• It has the lower heat transfer coefficient than the other types for not having liquid circulation

• Used for fouling materials and vacuum operation with a rate of vaporization up to 80% of the feed

65Boiling heat transfer and pool boiling

Nucleate pool boiling

Critical heat flux

Film boiling

66

Nucleate

boiling heat

transfer

coefficient

67

Critical flux

heat transfer

coefficient

Film boiling

heat transfer

coefficient

Convection boiling 68

Effective heat transfer coefficient encounter the

effect of both convective and nucleate boiling

71Design of air cooler

73Mechanical Design for HE

A typical sequence of mechanical design procedures is summarized

by the flowing steps

• Identify applied loadings.

• Determine applicable codes and standards.

• Select materials of construction (except for tube material, which

is selected during the thermal design stage).

• Compute pressure part thickness and reinforcements.

• Select appropriate welding details.

• Establish that no thermohydraulic conditions are violated.

• Design nonpressure parts.

• Design supports.

• Select appropriate inspection procedure

74Design loading

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